fix: v2.6.1 — panes start in their folder again after an update (#69), Changes panel stacks every repo, clickable paths in chat

- #69: tmux applies a pane's `-c` only while its server's own cwd exists.
  The server was forked from the dashboard's cwd (the plugin cache dir),
  outlives updates, and the old cache dir is pruned — after that every new
  pane started in a deleted directory, where `claude` died at once ("run not
  found") and a shell printed getcwd errors. tmux calls now run from `/`,
  and the pane's sh wrapper cds into its folder itself, which also heals a
  tmux server that is already stuck.
- Changes panel: a workspace's extra folders are sections stacked under the
  workspace folder (VS Code Source Control style), with Close repository /
  Close other repositories on a header's right-click.
- Chat: URLs and absolute paths are links; Claude Code's `[Image: source:]`
  line folds into its turn; uploads under `<data dir>/drops/` are listed.
- Update check: a checkout holding commits a newer release lacks reports
  `diverged_from_release` instead of offering a fast-forward that can only fail.

server/__tests__/api.test.js

@@ -3100,7 +3100,7 @@ describe("GET /api/sessions/:id/outline", () => {
       hook_type: "UserPromptSubmit",
       data: {
         session_id: sid,
-        prompt: `compare these ${drop}\n/tmp/agenthub-drops-1000/fedcba9876543210.png`,
+        prompt: `compare these ${drop}\n/home/u/.claude/agenthub/drops/fedcba9876543210.png`,
       },
     });
     const mem = "/home/u/.claude/projects/-w/memory/release.md";
@@ -3113,7 +3113,7 @@ describe("GET /api/sessions/:id/outline", () => {
     await pre("Write", { file_path: mem, content: "x" });
 
     const { body } = await fetch(`/api/sessions/${sid}/outline`);
-    assert.deepEqual(body.uploads, ["/tmp/agenthub-drops-1000/fedcba9876543210.png", drop]);
+    assert.deepEqual(body.uploads, ["/home/u/.claude/agenthub/drops/fedcba9876543210.png", drop]);
     // a.ts was read, then edited: an output, no longer a file it only used.
     assert.deepEqual(body.files, ["/w/src/c.ts"]);
     assert.deepEqual(body.memory, [mem]);